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rhombohedron; relating to a system of forms including the rhombohedron and scalenohedron. Rhombohedral iron ore (Min.) See Hematite. -- Rhombohedral system (Crystallog.), a division of the hexagonal system embracing the rhombohedron, scalenohedron, etc.

Calcium carbonate, or carbonate of lime. It is rhombohedral in its crystallization, and thus distinguished from aragonite. It includes common limestone, chalk, and marble. Called also calc-spar and calcareous spar.

A mineral occuring in glassy rhombohedral crystals, varying, in color from white to yellow or red. It is essentially a hydrous silicate of alumina and lime. Called also chabasie.

teral cleavage, cleavage parallel to the lateral planes. -- Octahedral, Dodecahedral, or Rhombohedral, cleavage, cleavage parallel to the faces of an octahedron, dodecahedron, or rhombohedron. -- Prismatic cleavage, cleavage parallel to a vertical prism.

A rhombohedral zeolitic mineral, related in form and composition to chabazite.

the sesquioxide, so called because of the red color of the powder. It occurs in splendent rhombohedral crystals, and in massive and earthy forms; -- the last called red ocher. Called also specular iron, oligist iron, rhombohedral iron ore, and bloodstone. See Brown hematite, under Brown.

An ocher-yellow mineral occurring on minute rhombohedral crystals. It is a hydrous sulphate of iron and potash.

Native magnesium carbonate occurring in white compact or granular masses, and also in rhombohedral crystals.

ng chiefly of the oxides of iron and titanium. It is commonly massive, but occurs also in rhombohedral crystals. Called also titanic iron ore, and ilmenite.

A glassy colorless mineral occurring in rhombohedral crystals, sometimes used as a gem. It is a silicate of glucina, and receives its name from its deceptive similarity to quartz.

A sulphide of arsenic and silver of a beautiful cochineal-red color, occurring in rhombohedral crystals, and also massive; ruby silver.

Ruby silver; dark red silver ore. It is a sulphide of antimony and silver, occurring in rhombohedral crystals or massive, and is of a dark red or black color with a metallic adamantine luster.

carbonate, a rose-red mineral sometimes occuring crystallized, but generally massive with rhombohedral cleavage like calcite; -- called also dialogite.

Rhombohedral.

A pyramidal form under the rhombohedral system, inclosed by twelve faces, each a scalene triangle.

ate of iron, an important ore of iron occuring generally in cleavable masses, but also in rhombohedral crystals. It is of a light yellowish brown color. Called also sparry iron, spathic iron.

A mineral occurring usually in three-sided or six-sided prisms terminated by rhombohedral or scalenohedral planes. Black tourmaline (schorl) is the most common variety, but there are also other varieties, as the blue (indicolite), red (rubellite), also green, brown, and white. The red and green varieties when transpare…